1. Field of the Invention
The present invention relates to a packaging film made of a stretchable polymer film material and having a multiplicity of holes on the main film.
2. Description of the Prior Art
For packing or wrapping goods stacked on a pallet, bales of straw, fruit, trolleys of pots of plants etc., it is known that perforated plastic stretch films are used in order to provide sufficient holding force and stretchability of the packaging film as well as ventilation of the products to be packed. Known from EP 0 820 856 A1 is a pre-stretched plastic stretch film in which holes are formed by a thermal irradiation method without contacting the film and thus without waste of film material, for example, caused by punching out holes.
Known from EP 0 909 721 A1 is a perforated extensible palletizing film comprising a longitudinally elongated thin sheet of extensible plastics provided with ventilation holes and longitudinal reinforcement elements which are made of extensible plastics and are adapted to increase the strength of the film in the pulling direction.
Similar perforated stretch films are known from DE 102 01 480 A1, WO 01/60709 A1 and WO 02/094674 A1.
The perforations of these stretch films represent a macro perforation in which holes having a diameter of at least 5 mm are provided in a base film. Films with significantly smaller perforations represent a micro perforation and are irrelevant to the present invention.
The above should not be confused with film products on which slits or small punctures have been made initially with the intention that these increase, break or open (resulting in large openings) as a result of the film being stretched during usage e.g. in a wrapping machine with a pre-stretching system.
A wrapping machine with a film pre-stretching system will pre-stretch the film prior to wrapping it on a pallet load by a pre-stretch ratio e.g. between 100 to 300%. Pre-stretching the film by 100% means that an initial length of 1 meter becomes 2 meters after stretching, i.e. a length increase of 100%. The stretching direction coincides with the main or longitudinal direction of the film. Alternatively, a packaging film may be provided already stretched to the length to be used by the end-user (i.e. stretched during the production or conversion process). In this case a wrapping machine without a pre-stretching system may be employed or, simply, the film may be applied to the load manually.
In both cases, partial or total failure (breakage) of the packaging film is undesirable.
In practice, a number of problems may arise in connection with the above-described macro-perforated stretch films comprising reinforcing elements or having no reinforcing elements. Namely, the stretch films are normally used by automatic or semi-automatic stretch wrapping machines, in order to wrap products stacked on pallets. As mentioned earlier, to ensure good material utilization, it is desirable to stretch the stretch film before or during the wrapping operation. To this end, considerable force is required to stretch the film which can be significantly increased by reinforcing elements fixed onto the stretch film. Under special conditions, a wrapping machine is no longer capable of providing sufficient stretching of the stretch film for lack of sufficient power.
On the other hand, if the wrapping machine is strong enough to provide the desired stretching, there is the danger that the forces acting on the products to be wrapped are too great. If the products are, for example, boxes, there is the risk that the stretch film and/or the reinforcing elements fixed thereto, press the products or their packages together and damage them.